Continuous flow heater for liquids



Aug. 27, 1968 K. ZANGL 3,398,721

CONTINUOUS FLOW HEATER FOR LIQUIDS Filed July 1. 1966 I NVENTOR. KARL Z/l/l/GA ATTUEA/EKS' United States Patent O "ice 3,398,721 CONTINUOUS FLOW HEATER FOR LIQUIDS Karl Zangl, Kantstrasse, 8 Munich 13, Germany Filed July 1, 1966, Ser. No. 562,320 Claims priority, application Germany, July 1, 1965, Z 11,627 Claims. (Cl. 122-33) ABSTRACT OF THE DISCLOSURE A continuous flow heater having a first fluid circuit containing a use liquid therein, preferably water. The first fluid circuit is maintained at a pressure substantially above atmospheric pressure whereby the use liquid can be discharged from the circuit at a temperature higher than the atmospheric boiling temperature of the liquid. Pressurized feed means are provided for supplying additional use fluid to the circuit and for maintaining the fluid in the circuit at the desired pressure level. A second fluid circuit having a heating liquid therein, preferably oil, is used to heat the use liquid in the first circuit. The normal operating temperature of the heating liquid in the second circuit is greater than the discharge temperature of the first fluid but less than the atmospheric boiling temperature of the heating fluid.

This invention relates to a continuous flow heater utilizing both a liquid heating medium and a use medium. Said heater has an at least partially double-walled housing whose double wall forms a flow channel comprising the flow path of the heating medium and wherein a coil of pipe is arranged through which a use medium can flow to be heated to the desired outlet temperature.

In a known continuous flow heater of the afore-mentioned type (German Patent No. 1,937,729), there is provided a housing in the form of a cylindrical overflow storage reservoir for the use medium which is constructed with a double wall at the cylinder jacket surface. The overflow is in contact with the coil of pipe in the flow channel formed by the double wall for the use medium. This continuous flow heater can heat use media close to their boiling point without provision of special precautions. However, should the use medium be heated higher than to its boiling point, the continuous flow heater provided for such a case is subject to special control and fabrication requirements, which increases both its initial cost and its cost of operation.

However, it is desired especially for vulcanizing plants to feed the pressure hoses of tire repairing equipment, instead of with compressed air as use medium, with hot water having a temperature of about 130 C. whereby to increase the economy of the plant by speeding the vulcanizing process. The achievable profit, however, would be minimized or completely destroyed by increased maintenance and operating costs of a hot-water plant subjected to the requirements of the steam boiler regulations.

Furthermore, a continuous flow heater is known (German publication specification No. 1,109,343) in which there is provided a first coil of pipe through which the use medium can flow in the internal zone of the double-wall housing, while the heating medium flows through a second coil of pipe, which is positioned in the flow channel formed by the double wall of the housing. From said second coil of pipe the heat is transmitted to the circulating medium flowing through the interior of the housing, said circulating medium flows around and heats a reservoir for the use medium or rather flows around and heats a first coil of pipe through which said use medium flows. Such an indirect heat exchange requires a high tmperature of the heating medium and results in a low efiiciency of the con- 3,398,721 Patented Aug. 27, 1968 tinuous flow heater which must be dimensioned larger for higher hourly output. Therefore, said known continuous flow heater especially if constructed as a reservoir through which a use medium flows is not suitable to serve vulcanizing plants economically which require a greater supply of use water of a temperature of about 130 C.

Therefore, it is the purpose of the invention to provide a space-saving, continuous flow heater of the above-mentioned type, which at a high efliciency makes possible safe heating of a use medium to a temperature exceeding its normal boiling point and which provides a high hourly output. In order to achieve this, the continuous flow heater according to the invention utilizes a high pressure pipe system which forms, together with a coil of pipe, a continuously closed circulation system, from which the use medium can be taken or to which same can be added at a superatmospheric pressure corresponding to a boiling point higher than the outlet temperature. Said heater is further characterized by control elements provided to maintain said superatmospheric pressure within the circulation system, by the use of a coil of pipe which is placed within the cross-sectional area of the flow channel whereby the respectively adjacent outer pipe surfaces of the pipe cooperate to define a space forming a curved guide channel extending lengthwise of the entire coil of pipe and finally, by devices impelling the heating medium forceably through the guide channel.

In the continuous flow heater according to the invention, the superatmospheric pressure in the circulation system of the use medium can be maintained at a magnitude independent of pressure variations in the water pipe circuit and independent of the respective outlet amount of discharge and yet prevents any steam formation. By means of a direct contact of the heating medium with the coil of pipe through which the use medium flows in the narrow guide channel of the continuous flow heater, said heater is of high efliciency and is of small dimensions even for high hourly outputs. If water is used as use medium, same can be heated without danger within the circulation system to over C. and can be taken out in large quantities, for instance to supply a vulcanizing plant. Thermo-oil can be used as a heating medium which for instance can be heated up to 250 C. and which assumes for a small continuous flow heater the obtaining of large quantities of use water with a temperature of about C.

For a further advantageous development of the invention it is suitable that a second coil of pipe is included in a known manner in the flow path of heating medium, that same is arranged inside of the housing, and that a burner can be attached to the housing in a way that the axis of the burner nozzle extends essentially coaxially with respect to the coils of the second coil of pipe. Since heat losses can be best minimized in the flow path of heating medium, a directly heated continuous flow heater can be constructed in a highly space-savin g manner and with a high efliciency.

Further characteristics and advantages of the invention will be understood from the following description in connection with the enclosed drawing, the single figure of which illustrates a schematic side view of a continuous flow heater according to the invention.

According to the drawing, a continuous flow heater of the invention can be provided with one at least partially double-walled cylindrical housing 1, whose double wall 2, 3 forms an annular flow channel 4 included in the flow path of the heating medium. The double wall of the housing 1 can be constructed of two pipes 2, 3 arranged concentrically with respect to each other, of different diameters which are connected close to their ends by flanges 5, 6.

A coil of pipe 7, through which the use medium flow,

extends spiral-like and is arranged in the flow channel 4. The coil of pipe 7 has an outer diameter which essentially is the same as the space between the pipes 2, 3. Consequently, the coil of pipe 7 essentially occupies the cross section of the flow channel 4. The respectively adjacent outside walls of the helix of pipe provide a space therebetween which forms a spiral-like guiding channel 4a extending lengthwise of the entire coil of pipe 7. The heating medium flows through said guiding channel 4a as described more in detail hereinafter.

The coil of pipe 7 is included in a high pressure pipe and circulation system 8, from which the use medium, for example water, with a superatmospheric pressure increasing its boiling point over the outlet temperature can be added by a feed line 9 or can be taken out by outlet valves 10.

To maintain constant pressure of the necessary magnitude in the circulation system 8 independent of pressure variations in the water pipe system and independent of the discharge amount, control elements are connected to the circulation system 8, for example in form of a pressure tank 11 and a pressure switch 12 which control a feed pump 13. The pressure line of said pump is connected through a check valve 15 to the feed line 9, while the suction line 16 is connected to an overflow tank 17. The latter can receive low pressure return water or tap water to feed the feed pump 13. The circulation system 8 is advantageously provided with a circulating pump 18 with a check valve 19 to guarantee a positive circulation of the use medium in direction of arrow 20, 21.

The heating medium flows in a circulation path which essentially is formed by the flow channel 4, the ends of which are connected by connecting lines 22. A second circulating pump 23 guarantees a positive circulation of the heating medium in direction of arrow 24.

Since the inner diameter of the annular fiow channel 4 corresponds essentially to the outside diameter of the coil of pipe 7, the heating medium is impelled through the spirally extending guiding channel 4a between the pipe windings, by which same are acted upon and heated by heating medium equally throughout the entire length. By this a rapid heat exchange of high efliciency is assured between heating and use medium.

According to the figure, a second spiral coil of pipe 25 can be connected in the connecting lines 22 and same can be arranged in the interior of the housing 1. Furthermore, a burner 26 can be attached to the housing in a way that the axis of the burner nozzle extends essentially coaxially with respect to the second coil of pipe 25. The flame or combustion gases from the burner 26, which enter the interior of the housing 1 and which leave same through an exhaust pipe 27, act upon the inside wall of the pipe 3 and also act upon the second coil of pipe 25. Such a directly heated continuous flow heater can be constructed to have high capacity and small dimensions.

A high efiiciency is guaranteed if, according. to the figure, the second coil of pipe 25 is provided with two concentric and countercurrent coils of pipe 28, 29 of different coil diameters, which are connected at the exhaust end of the housing 1 and which are connected at their free ends to the connecting lines 22 in a way that the heating medium flows through the inner coil of pipe 28 in a direction counter to the direction of flow of the combustion gases. The temperature of the heating medium is kept constant by a thermostat switch 30 which is arranged for controlling the burner 26 in the flow path. of the heating medium.

Furthermore, by means of magnetic valves 31, 32, 33 a heating coil 34 can be inserted into this flow path which is arranged inside of the overflow tank 17. A second thermostat switch 35 is arranged at the overflow tank, which controls the magnetic valves 31, 32, 33 in a way that the heating coil 34 is connected in the connecting lines 22 respectively if the temperature of the use medium storage in the tank reservoir 17 drops to the valve preset at the thermostat switch 35. Besides the heating coil 34, which can be connected by the connecting lines 22' to the connecting lines 22, radiators (not shown in the figure) of a conventional heating plant can be connected in the flow of heating medium.

To make possible an essentially pressureless circulation of the heating medium, the heating medium must operate at a boiling point which is essentially above the outlet temperature of the use medium. For this, for example, thermo-oil is suitable which can be heated up to 250 C. without forming appreciable pressure. Most of the commercial thermo-oils, however, act as an electrolyte by simultaneous wetting of iron and non-ferrous metal and by forming galvanic cells tend to cause decomposition of said different metals. Nevertheless, the pipes and walls, which are acted upon by the combustion gases of the burner of the directly heated continuous flow heater, including the heater of this invention, must be made of iron while the water pipes as usual are made of nonferrous metal or of alloys of same. To prevent a wetting of said different metals, the outside and inside wall of the pipe forming the coil of pipe 7 for the use medium can be constructed of different materials 7a, 7b, respectively. For making such a coil of pipe a copper liner may advantageously be inserted snugly into a steel pipe and the composite pipe is then bent to form a spiral. The thermo-oil then comes in touch only with structural elements of iron during its flow through the fiow path of the heating medium.

For the following explanation of the above-described continuous flow heater it is assumed that thermo-oil is used as a heating medium and water as a use medium, which latter is guided intermittently to a vulcanizing plant at a temperature of 150 C. Furthermore, it is assumed that the burner 26 is started by the thermostat switch 30 in a conventional manner it the temperature of the circulating thermo-oil drops below the value necessary to heat the use water to the desired heat level, for example, 250 C. The heating coil 34 is connected in the circulation path by the thermostat switch 35 until the use water storage of about 1000 liters is heated to about C. in the storage tank 17. When hot use water is taken out of the circulation system 8, the pressure in said system drops, for example from six atm., suddenly to a lower value, which, nevertheless, is suificiently high to prevent any formation of steam. The pressure switch 12 responding to the pressure drop closes the circuit for the feeding pump 13. Said pump 13 pumps use water of 80 C. into the circulation system 8 until the pressure in same returns to the six atm. In the continuous flow heater, only an increase of the average temperature which is caused by the water of 80 added to the circulation system 8 is needed.

The continuous flow heater according to the invention makes it possible in the above-described manner to heat 720 liters of water, which flows into the storage tank 17 at a temperature of about 10, in about 60 minutes to 60. By taking out the same amount and by using the same amount of oil a heater water tank of conventional construction can only achieve a use water temperature of 45 C. Said comparison shows a 40 percent higher efliciency of the continuous fiow heater of the invention.

Although the drawing and the description refer to a preferred example of construction of a continuous flow heater of the invention, same can be used in varied form within the scope of the appended claims. The heating and use media can be chosen freely and the circulation systems can be arranged with varying pipe connections on both sides or partially beneath the continuous flow heater housing. Furthermore, all constructional details of the drawing and the corresponding description can be inventive individually and also in any desired combination.

The embodiments of the invention in which an exclusive property or prividege is claimed are defined as follows:

1. A continuous flow heater comprising:

first fluid circuit means containing a liquid use medium therein; second fluid circuit means containing a liquid heating medium therein, said heating medium having an atmospheric boiling temperature which is higher than the atmospheric boiling temperature of said use medium; pressure means including control means for maintaining the use medium in said first circuit at a pressure substantially in excess of atmospheric pressure;

heat exchanger means including a portion of said first circuit means and a portion of said second circuit means for heating said use medium by said heating medium, said heat exchanger heating said use medium to a temperature higher than its atmospheric boiling temperature but less than its pressurized boiling temperature;

said heat exchanger including a partial double-Walled housing having inner and outer walls defining a space therebetween;

said portion of said first-circuit means comprising a substantially helically wound pipe through which the use medium can flow positioned within said space, said pipe having a size substantially equal to the width of the space between said inner and outer 'walls for almost completely filling same, adjacent coils of said helically wound pipe being spaced apart to define a substantially helical guide channel therebetween;

said portion of said second circuit means including said helical guide channel as defined by said coils and as additionally defined by the inner and outer walls of said heat exchanger housing;

discharge means connected to said first circuit means tfOl permitting discharge of said liquid use medium from said first circuit means at a discharge temperature higher than the atmospheric boiling temperature of the use medium;

feed means for supplying use medium to said first circuit means whenever use medium is discharged from said first circuit means; and

heating means for heating said heating medium to a temperature which is lower than its atmospheric boiling temperature but higher than the discharge temperature of the use medium.

2. A continuous flow heater as defined in claim 1, wherein said liquid heating medium comprises oil.

3. A continuous flow heater as defined in claim 2, wherein said liquid use medium comprises water.

4. A continuous flow heater as defined in claim 1, further including an overflow tank connected to said first circuit means, and said feed means including a pump controlled by said control means for supplying use medium to said first circuit means.

5. A continuous flow heater as defined in claim 4, wherein a hollow coil is positioned within said overflow tank, and means operatively interconnecting said coil to said second circuit means for permitting the heating medium to flow through said coil for heating the use medium in said tank.

6. A continuous flow heater as defined in claim 1, wherein said second circut means defines a closed flow path for said heating medium, and thermostat means operatively associated with said second circuit means for controlling said heating means.

7. A continuous flow heater as defined in claim 1,

wherein said heat exchanger housing is formed by inner and outer concentric pipes of different diameters, flanges being positioned adjacent and connected to opposite ends of said pipes for closing said housing, and said helically wound pipe of said first circuit means extending spirallike in a lengthwise direction between said pipes.

8. A continuous flow heater as defined in claim 7, wherein said helically wound pipe has an outside coil diameter substantially equal to the inside diameter of said outer pipe comprising the outer housing wall.

9. A continuous flow heater as defined in claim 1, wherein said second circuit means includes a second portion which comprises a spiral-like coil of pipe with said heating medium flowing therethrough, said spiral-like coil of pipe being positioned within the interior of the housing as defined by the inner wall thereof, and wherein said heating means comprises a burner positioned adjacent the housing with said :burner having a burner nozzle extending substantially coaxial with respect to the helix of said spiral-like coil of pipe for heating the heating medium therein.

10. A continuous flow heater as defined in claim 9, 'wherein the second portion of said second circuit means includes inner and outer concentric and counterwound coils of pipe having different coil diameters connected to each other adjacent one end of said housing, said burner being positioned adjacent the other end of said housing.

11. A continuous flow heater as defined in claim 10, wherein the heating medium flows through the inner coil of pipe in a direction toward the burner.

12. A contniuous flow heater as defined in claim 1, wherein said control means includes a pressure tank connected to said first circuit means and a pressure switch assooiated therewith for controlling and maintaining the pressure of said use medium in said first circuit means above atmospheric pressure.

13. A continuous flow heater as defined in claim 1, wherein circulating pumps are connected to both said first circuit means and said second circuit means for circulating said use medium and said heating medium, respectively.

14. A continuous flow heater as defined in claim 1, wherein an overflow tank is operatively associated with said first circuit means rfor receiving use medium therein, pipe means positioned within said overflow tank, valve means positioned between said pipe means and said second circuit means for permitting said pipe means to be interconnected with said second circuit means, and thermostat means operatively associated with said overflow tank for controlling said valve means whereby opening of said valve means permits said pipe means to be interconnected with said second circuit means whereby heating medium is allowed to flow through said pipe means for heating the use medium contained in said overflow tank.

15. A continuous flow heater as defined in claim 1, wherein the helically wound pipe ofr said first circuit means has inside and outside walls of respectively diiferent materials.

References Cited UNITED STATES PATENTS 3,060,905 10/ 1962 Cunningham, et a1.

122248 XR 3,236,211 2 1966 Okaniwa 12233 3,295,605 1/ 1967 Sebald 122-406 XR KENNETH W. SPRAGUE, Primary Examiner. 

